A portable electronic device such as a cellular phone generally uses a battery pack in which a battery that supplies power to the unit is mounted. When the battery does not function sufficiently even though the battery has been charged, it is possible to replace the battery pack in order to continue using the electronic device. Here, a typical battery pack uses a rechargeable secondary battery such as a Lithium-ion battery as the battery and integrates it with an overcharge-prevention circuit or over-discharge-prevention circuit. When the remaining amount of time that this kind of secondary battery can be used becomes short (or in other words, when the battery life becomes short), or when it become impossible to charge the battery to a specified voltage, or when due to some kind of trouble the battery is not able to supply a specified amount of power to the device, the battery pack is replaced with a different battery pack, which is mounted and used in the device.
While charging the battery, the battery pack become hot, so in order that the battery pack does not exceed a specified temperature, the temperature of the battery pack may be monitored from the side of the electronic device. In other words, when charging the battery by supplying power to the battery from the power supply that is connected to the electronic device, output data from a temperature-detection sensor that is contained inside the battery pack near the battery is monitored, and when the temperature exceeds a preset specified temperature, charging stops, and an alarm is displayed. Also, during use as well, abnormalities that may occur in the battery, and the temperature of the battery pack may be monitored periodically. In this case, a terminal for obtaining the output data related to the temperature from the battery pack is necessary, and it can be located on the battery pack or on the electronic device.
Also, technology is known by which the battery pack is authenticated in order to identify whether or not the battery pack is a proper battery pack. In other words, both the battery pack and the electronic device store an ID (identifier), and when connected, the battery pack is authenticated as to whether it is a proper battery pack by comparing the ID output from the battery pack with the ID stored in the device. Recently, due to counterfeit and imitation battery pack parts, there is a possibility that problems such as abnormal heat, leakage, cracking or the like may occur. Therefore, in addition to having a temperature detection function, it is desirable that the battery pack have a authentication function.
When obtaining this kind of ID signal, it is generally necessary to have a new terminal or signal line. In that case, the number of parts increases or the mounting area is enlarged. Therefore, a device is known that is constructed such that the data-transmission signal for authentication when authenticating the battery pack, and the signal from the temperature-detection sensor are sent on one signal line in order to suppress the increase in the number of parts and enlargement of the mounting area. (For example, see patent document 1.)
FIG. 7 is a block diagram showing the construction for sharing the transmission line of the temperature-detection sensor in the data-transmission circuit of a conventional device, and the communication line of a clock. In FIG. 7, when measuring the resistance of the thermistor (temperature-detection sensor) TH, the transistor T is ON, and the divided voltage of the resistance R and the thermistor TH with respect to the power supply V is applied to the communication line. The value of a divided voltage is input to buffer B1, and the temperature is detected by reading the value by a circuit (not shown in the figure) on the side of the electronic device. On the other hand, when performing authentication, the transistor on the side of the device is OFF, and the enable signal E1 is activated. Also, a clock CLK is sent from a buffer TB to a buffer B2 on the side of the battery. By doing this, it is possible for the transmission signal of the clock during authentication and the signal from the temperature-detection sensor to share one signal line.
[Patent Document 1] Japanese Patent Kokai Publication No. JP-P2003-162986A (FIG. 6)